Thermal-hydraulics in uncovered core of light water reactor in severe core damage accident. (II) Analysis of Power Burst Facility severe fuel damage scoping test with SEFDAN code.

Abstract

The SEFDAN is a computer program to analyze the one-dimensional thermal-hydraulics of a partially uncovered core of a light water reactor in a severe degraded-cooling event. In order to verify the code and to obtain better understanding of the severe core damage process, SEFDAN has been applied to analyses of the thermal response of fuel rods in the Power Burst Facility Severe Fuel Damage Scoping Test. This paper presents the calculated results and discusses, based on the results, on the phenomena that are important for prediction of the thermal response of fuel rods to a severe accident under the partially un-covered core condition. The calculated results are in good agreement with the experimental results. Namely the dry-out time of each elevation and the temperature behavior in both the slow heat-up and rapid temperature excursion processes are well simulated. The analysis indicates that fuel cladding temperature of the upper part of the test bundle would have reached the melting point of ZrO2 and fuel center line temperature would have reached the melting point of UO2 during a rapid temperature excursion which was caused by rapid decreasing of the dry-out level and accelerated by zirconium-water reaction in the lower part.